1. Field of the Invention
The invention relates to thermoplastic molding compounds comprising functionalized polyphenylene ethers and polyamides.
2. Discussion of the Background
Polyphenylene ethers (PPE) are high-grade engineering thermoplastics having high melt viscosities and softening points. They are primarily used where stability at high temperatures is important (cf. U.S. Pat. No. 3,306,874, U.S. Pat. No. 3,306,875, U.S. Pat. No. 3,257,357, and U.S. U.S. Pat. No. 3,257,358). Of course, molded parts made of pure polyphenylene ether are brittle due to their poor impact resistance, and the solvent resistance is unsatisfactory; therefore, other thermoplastics are usually added to mixtures containing polyphenylene ethers.
Admixtures of polyphenylene ethers with polyamides exhibit good solvent resistance and good flowability (DE-A 16 94 290 and JP-OS 78/47 390). Usually, however, brittle products are obtained, since the two components are incompatible. Aromatic polyamides, as added for example in accordance with EP-A 0 131 445, are difficult to process with polyphenylene ethers. Greater compatibility of the two phases is achieved by means of a functionalization of polyphenylene ethers, e.g. with maleic acid anhydride in the presence of radical formers (JP-A 84/066 452). To be sure, this advantage is bought at the expense of a partial gelation of the PPE phase.
Therefore, it was proposed that the compatibility of both polymers be increased by adding an adequate quantity of a flow agent, e.g. an organic phosphate (EP-A 0 129 825) or a diamide (EP--OS 0 115 218). However, the improved compatibility is in contrast with a significantly reduced heat resistance. Molding compounds whose copolymers comprise styrene and unsaturated acid derivatives (EP-A b0 046 040) exhibit the same drawback.
The object of EP-a 0 0224 120 are resin compounds, which comprise a polyphenylene ether, a polyamide, a third component and, if desired, high-molecular rubbers. A liquid diene-based polymer, an epoxide, or a compound having a double or triple bond and a functional group (such as acid, anhydride, ester, amino or alcohol group) is added as the third component. However, the toughness of the resin compounds obtained is inadequate for many applications.
The process described in JP-A 84/86 653 radically grafts 100 parts of polyphenylene ether with 10 to 300 parts of a mixture containing 50 to 99% styrene and 50 to 1% of unsaturated carboxylic acids or anhydrides and admixes the product with polyamides. Of course, the resulting molded parts exhibit good mechanical properties; yet due to the noticeable proportion of polystyrene there is a negative effect on the heat resistance.
In EP-A 0 185 054 the functionalization of polyphenylene ethers is described by means of the conversion of polymers with hydroxypolycarboxylic acids or their derivatives in the melt. After admixing the polyamides, molding compounds are obtained from whose elongation at break and notched impact strengths one may infer a non-satisfactory bonding at the phase boundaries.
The object of EP-A 0 195 815 is the functionalization of polyphenylene ethers with trimellitic anhydride acid chloride in solution. The blends with polyamides tend to be better than in the previous cases; yet the result of the described functionalization is that either hydrogen chloride or --with the addition of a tertiary amine--noticeable quantities of ammonium chlorides form and thus corrosion problems occur. In this case the economically interesting direct isolation of polyphenylene ethers by means of removing the solvent cannot be applied.
In EP-A 0 211 201 a composition of polyphenylene ethers and polyamides is described that is prepared by capping the terminal OH groups of the polyphenylene ether and then polymerizing with a lactam. In this case the capping agent acts as a promoter for the polymerization of the lactam.
Suitable promoters are maleic acid anhydride, cyanogen chloride, N,N'-carbonyldiimidazole, phenylchloroformate and other strong Lewis acids, which are at least bifunctional. However, in practice these compositions are not satisfactory. The functional groups of the promoters are chemically unstable, and the restriction to polyamides, which are obtained by means of the polymerization of lactams, is perceived as limiting.
From the DE-A 36 00 366 thermoplastic molding compounds are known in which the important components are polyphenylene ether, a compatibilizing polymer as a main chain and polyphenylene ethers as side chains, a functionalized polyethylene and a polyamide. Thus it is quite a complex blend in which each of the four components is essential in order to assure not only good compatibility but also high impact resistance and heat resistance. It would be desirable to attain these goals in a simpler manner.
The DE-A 36 15 393 and DE-OS 36 21 805 describe molding compounds that contain a remelted pre-formed compound, in addition to a polyamide. The pre-formed compound comprises a polyphenylene ether, a polyoctenylene and at least one acid component such as maleic acid anhydride. Thus, in both cases it is also mandatory that the polyphenylene ether be remelted with a strong acid component and a toughening agent be added in order to attain a qualitatively satisfactory level of notch impact strength; a similar process is described in EP-A 0 232 363.
Thus the molding compounds known from the literature of prior art can be prepared only in an expensive manner, or the properties of molded parts that are manufactured from them are unsatisfactory.